In large buildings such as multi-story office buildings it is common practice to have a central air conditioning system provide cooled air throughout the building. It is likewise common practice to provide a heating system for the periphery of the building while the core of the building is heated as a by-product of the lighting and equipment as well as the personnel present. In such a situation a cooling demand may occur in the core of the building while the periphery is being heated so that both systems are concurrently in operation and therefore it is necessary that both systems be enabled.
Although current Federal guidelines for heating and cooling temperatures would normally preclude simultaneous heating and cooling in a zone, factors such as sun load may create localized aberations that can cause a cooling demand in a zone that is being heated. This problem is aggravated by the locking of thermostats and having zones that are part in the sun and part shaded. Additionally, because the air conditioning system would respond to the heat from a fire to produce additional ventilation, it is desired, and even required by some building codes, that the air conditioning units be capable of selective disabling in the case of fire. Where rooms and offices are not in use it is likewise desirable that the cooling system be disabled as to the unused areas.
In air distributing arrangements where system pressure is serially passed through a filter and regulator and thence to a bladder and bleed-type thermostat, the bleed-type thermostat controls the inflation of the bladder which coacts with the cutoff plates to control the amount of cooled air entering the room. Normally, such an arrangement would keep the air conditioning system disabled if the heating system were operational and if the Federal guidelines were being observed.